Because of its excellent photographic properties such as sensitivity and gradation adjustment (as compared to other photographic processes such as electrophotography and diazo process), the process using silver halide has heretofore been most widely used. In recent years, a new process has been developed by which images can be easily and rapidly obtained on a silver halide light-sensitive material. This was accomplished by using a heat development requiring no developing solution rather than the conventional wet process in which a developing solution is used at near normal temperature.
A heat-developable light-sensitive material is well known in the art. Examples of a heat-developable light-sensitive material and heat development process are described in Shashinkogaku no Kiso (Corona Co., Ltd., 1979), pp. 553-555, Hakko Eizo Joho, April, 1978, p. 40, Nebletts Handbook of Photography and Reprography, 7th Ed., Van Nostrand Reinhold Company, pp. 32 and 33, U.S. Pat. Nos. 3,142,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108 and 1,167,777, and Research Disclosure, No. 17029, June, 1978, pp. 9 to 15.
Many processes have been proposed which use a heat development process to obtain color images. In connection with a process for the formation of color images by the combination of an oxidation product of a developing agent and a coupler, many compounds have been proposed. For example, a combination of a phenylenediamine reducing agent and a phenolic or active methylene coupler is described in U.S. Pat. No. 3,531,286. A p-aminophenol reducing agent is described in U.S. Pat. No. 3,761,270. Sulfonamidophenolic reducing agents are described in Belgian Pat. No. 802,519 and Research Disclosure, September, 1975, pp. 31 and 32. A combination of a sulfonamidophenolic reducing agent and a 4-equivalent coupler is described in U.S. Pat. No. 4,021,240.
In connection with a method for the formation of positive color images by a light-sensitive silver dye bleach process, many processes have been proposed. For example, examples of useful dyes and bleach processes are described in Research Disclosure, No. 14433, April, 1976, pp. 30 to 32, and 15227, December, 1976, pp. 14 and 15, and U.S. Pat. No. 4,235,957.
Furthermore, an image formation process involving a heat development process which utilizes a compound which has previously possessed a dye portion and is capable of releasing a mobile dye in response or counter response to the reduction reaction of silver halide to silver at an elevated temperature is disclosed in European Pat. Nos. 76,492A and 79,056A and Japanese Patent Application (OPI) Nos. 28928/83 and 26008/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
Such a heat-developable light-sensitive material undergoes development upon heating. However, such a heat-developable light-sensitive material is disadvantageous because after the material is heated to the necessary temperature, it takes a great deal of time for the material to cool down. The lengthy cool-down period causes overdevelopment which may lead to an increase in fog. Such a heat-developable light-sensitive material is also disadvantageous for another reason. When a dye produced or released in a lightsensitive element is heat-transferred to an image-receiving element, the heating required for the transfer process causes overdevelopment which may lead to an increase in fog on the transfer images. Furthermore, it is difficult to heat uniformly the light-sensitive material to an elevated temperature. This heating is an uneven heating temperature which is undesirable. However, if the light-sensitive material is uniformly heated, uneven amounts of water or of an image formation accelerator (such as base) remain in the light-sensitive material. These difficulties may cause a non-uniform progress of development or dye transfer, resulting in an uneven image which lowers the picture quality.